Since dynorphin A1-17 has been shown by previous studies to be presumably the major endogenous kappa ligand and its effects would be shared by both the shorter dynorphin A1-13 as well as the shorter and stabilized dynorphin A1-10 amide, we are conducting studies of the effects of these dynorphin A peptides in normal volunteer subjects both to determine the effects on hormones of the hypothalamic-pituitary-adrenal axis, as well as hormones of the hypothalamic-pituitary-gonadal axis, prolactin, and other neuropeptides and neuro-transmitter systems and their effects on immune function.